Both Donald Trump and Hillary Clinton pose very real threats to Democracy and peace, but for different kinds of reasons.
The US has always pursued its economic/political interests in aggressive ways regardless of which party occupies the White House. The US has never shied away from supporting the worst kinds of dictators; and while for decades they used the excuse of "communism" as their primary reason for supporting leaders and regimes that clearly were not democratic, for the past couple of decades they haven't really used any excuse, they just know where their geo-political interests are and they act accordingly. Thus, during the Cold War they could support awful regimes like the Shah in Iran, or Suharto in Indonesia, and they did so as part of a supposed political struggle against Bolshevism or Maoism. But since the end of the Cold War, the US has continued to support a host of authoritarian regimes without any meta-narrative concerning Russian or Chinese aggression. These regimes include brutal governments in Thailand, Saudi Arabia, Qatar, Jordon, Cameroon, Egypt, and many others. There is really no active excuse used by the US government for such support except the complex game of geopolitics.
Hillary Clinton (along with the past two Democratic Presidents, Bill Clinton and Obama) has played an active and integral part in this international attack on democracy. As a member of a very real two party oligarchy, Clinton has been no less of a so-called "hawk" than many of her Republican opponents.
And as president, Hillary Clinton would continue to pose a threat not only to democracy, but to world peace. Clinton supported the wars in Afghanistan and Iraq, the two conflicts that have seriously destabilized the Middle-East and the world in general. And because Clinton is part of a long-standing geopolitical hierarchy that asserts certain perceived US interests against both Russian and Chinese power, she could easily nudge the world into a global, and possibly nuclear, conflict in a number of sensitive locations. Just yesterday the Washington Post was commenting about the dangers posed by a Clinton presidency, as Putin (whose power itself is shaky given the growing crisis in the Russian economy) threatens to use Russian aggression in Syria and possibly the Baltic States to not only "test" a newly inaugurated Clinton, but to use conflict with the West as a classic bait and switch on his own population which, predictably, would rally around the "motherland."
But while we have to acknowledge that Hillary Clinton poses a threat to democracy and peace (more or less a continuation of the threat that both the Democrats and Republicans have been posing for generations now), Trump poses an equal, albeit different kind of threat. Now, putting aside his sheer instability as a person and a potential leader (an instability that has manifested itself countless times during the past year), Trump seems more likely to cozy up Putin, an act that manifests its own kinds of dangers. For one thing, Trump has displayed radical anti-democratic tendencies. His talk of not accepting election results, of jailing opponents, his consistent attacks on the media (and his talk of gagging the media if elected), as well as his generally xenophobic and nationalist rhetoric, are all demonstrations of his threat to democracy. And Trump admires Putin, in part, precisely because he is a so-called "strong-man" leader who rules with an iron fist. Because of his admiration of Putin and the current de facto dictatorship in Russia, Trump is the type of man who, instead of generation conflict with Russia on an international scale, would very likely collude with Putin in efforts to control and subjugate burgeoning democratic efforts globally and simply pair up in a global geopolitical and economic effort to dominate the globe.
While the Democrat-Republican dominance of the US was far too ready to support dictatorships around the world in support of US interests, they also supported certain democracies and democratic efforts where they constituted a bulwark against their perceived enemies. US lawmakers and diplomates often knew that in some areas if they went too far in their anti-democratic efforts they always stood in danger of pushing people too far the other way, potentially towards Bolshevism, for example. But in today's geopolitical atmosphere, American collusion with Russia in places like Syria, the Baltic States, and other political hotspots would leave many nations extremely vulnerable and with little room to maneuver against such a brutal alliance. In other words, as bad as the US policies have been in the past under the de facto Democrat-Republican alliance, it would be unrealistic not to understand that the competition between the US and countries like Russia and China also acted as a wedge issue for some people to promote more democracy.
I suspect that Trump, in a surprising epiphany, has simply realized that it would be easier for the US to promote its interests of economic and political domination by just coming straight out with it and colluding with Russian aggression. From the point of view of a man like Trump, someone with clearly evident dictatorial ambitions, such an alliance just makes sense. In the past, when Russia represented a different kind of domination to the Western Capitalist Hegemonic variety, conflict with the Soviet Union was, perhaps, inevitable. But today, when Trump clearly would like to run the US in much the same way that Putin runs Russia, a geopolitical alliance would make more sense, particularly for those interested in straightforward economic and political domination.
Thus, it seems to me that Clinton and Trump both pose threats to democracy and international peace. So, from one point of view, there is very little to choose between them. On the other hand, if you are, for example Kersti Kaljulaid (the centrist, nationalist president of Estonia), or an anti-Asad rebel in Syria, Trump surely poses a more eminent threat.
Either way, the globe is presently a tinder box of conflict and democracy is under serious threat almost everywhere you look. What will happen next is anyone's guess.